1. Technical Field
The present invention relates to an in-vehicle radar device mounted on a vehicle such as automobile (hereinafter referred to as a vehicle).
2. Related Art
An in-vehicle radar device is a radar device of a so-called pulse radar type for emitting electromagnetic waves such as an electric wave and light towards the front side of a vehicle in a bundle (pulse form), and detecting information including a distance and a direction to an obstacle at the front side of an own vehicle based on the reflected wave from the front side of the vehicle. An electric field and a magnetic field include a static field, which is temporally constant, and a wave field which temporally fluctuates and propagates to a distant in space, where the wave field is referred to as a “electromagnetic wave”. The typical electromagnetic wave is an electric wave, but light, X-ray and the like are also electromagnetic waves.
The electromagnetic wave of pulse form emitted from a transmission unit of the in-vehicle radar device is reflected by a body surface (rear reflector or reflecting site corresponding thereto) of an obstacle at front of the own vehicle (hereinafter referred to as a leading vehicle for the sake of convenience), and received by a reception unit of the in-vehicle radar device. Assuming a time from an emission of the electromagnetic wave to a reception of the reflected wave is T, the distance L from the leading vehicle is given by “L=(T×velocity of light)/2”. The direction of the leading vehicle with the own vehicle (vehicle installed with in-vehicle radar device) as a reference is obtained in the emitting direction of the pulse-form electromagnetic wave, and for instance, the direction of the leading vehicle is obtained as 0 degrees if the emitting direction is 0 degrees (i.e., advancing direction of the own vehicle).
The related art of the in-vehicle radar device as described in Japanese Unexamined Patent Publication No. 2003-42757 for example is known. In this radar device, the laser beam, which is one type of electromagnetic wave, is emitted in pulse-form for every one unit region of a horizontal scan (monitoring region in the horizontal direction at the front side of the own vehicle, that is, region segmentalized from a horizontal scanning region, hereinafter referred to as a horizontal scanning unit region), a distance to the leading vehicle is obtained from the time until receiving the reflected wave from an obstacle such as the leading vehicle, and a direction of the leading vehicle is obtained from the scan angle (horizontal scan angle) of the horizontal scanning unit region of when the reflected wave is obtained.
According to the principle described above, the in-vehicle radar device detects the distance and the direction to the obstacle (leading vehicle etc.) in front of the vehicle, but the reflected wave also includes reflected wave from that which should not originally be detected as an obstacle such as road surface, in which case, the road surface may be wrongly detected as false obstacle.
In the related art, focusing on the difference in the waveform of the reflected wave from the leading vehicle and the reflected wave from the road surface, more specifically, on the fact that the intensity of the reflected wave from the leading vehicle is greater than that of the reflected wave from the road surface and that the duration time (spread of the base of the reflected waveform) of the reflected wave from the leading vehicle is shorter than that of the reflected wave from the road surface, a mechanism for distinguishing them (leading vehicle and road surface) based on such differences is disclosed (see paragraph [0040] and FIG. 5 of Japanese Unexamined Patent Publication No. 2003-42757).